This invention relates to thick film capacitors and more particularly is related to thick film capacitors which can compensate for changes in temperature which may occur that possibly affect the operational value of the electrical components in a circuit.
Existing screen printed capacitors are normally made by successively screening different layers of material on a suitable substrate such as alumina. Generally, one electrode is the first layer comprising a high temperature fired conductor while the second layer is a specially prepared insulator to form the dielectric. Over the dielectric a lower temperature fired conductor is screened to form the second electrode.
Typically, these capacitors can be made as separate electrical elements or, as generally desired, made with other elements such as resistors on a hybrid circuit. Because the dielectric layer must meet the requirements for a wide range of material capabilities and have the highest possible dielectric constant, it is generally not possible to produce a dielectric/conductor combination that will assure a zero temperature coefficient of capacitance (TCC).
A zero temperature coefficient of capacitance is generally desirable, because possible temperature changes in the circuit or the surrounding ambient conditions can cause undesirable variations in the value of the capacitor. These capacitance variations can cause undesirable effects on the electrical response of the circuit with the changing temperature. Consequently, it is desirable to provide a means to compensate for temperature variations of capacitance throughout certain ranges.
Typically, present screen printed capacitors do not have the ability to obtain zero temperature coefficient of capacitance, but do have the capability of producing a low temperature coefficient of capacitance value.